1. Field of the Invention
The present invention relates generally to a manufacturing method of a power transistor device with a super junction, more particularly, to a manufacturing method of a power transistor device with a super junction for adjusting the doping concentration of the super junction close to the sidewall of trench.
2. Description of the Prior Art
In power transistor devices, the ON resistance (RDS(on)) between the drain and the source is proportional to the power consumption of the device, so an effective way to reduce the power consumption of the power transistor device is to lower the RDS(on). In power transistor devices, the resistance provided by the epitaxial layer used for withstanding high voltage is the main contribution to the RDS(on). Although increasing the doping concentration of the conductive material in the epitaxial layer can reduce the resistance, the breakdown voltage of the epitaxial layer will also be lowered, thereby degrading the capacity of the power transistor device to withstand high voltages.
To maintain or increase the voltage withstanding ability of the power transistor device and to lower the resistance of the epitaxial layer, a power transistor device with super junction which has high voltage withstanding ability and low ON resistance has been developed in the industry. A conventional method of manufacturing a power transistor device is to form an N-type epitaxial layer on an N-type substrate, and an etching process is then performed on the N-type epitaxial layer to form a plurality of deep trenches. A dopant source layer is then filled into each deep trench and a high-temperature diffusion method is performed to diffuse P-type dopants in the dopant source layer into the N-type epitaxial layer so as to form a P-type doped region, wherein the N-type epitaxial layer and the P-type doped region constitute a P-N junction, i.e. the super junction, which is perpendicular to the substrate. However, the P-type doped region is formed by diffusion, thus the doping concentration will become higher when the doped region is closer to the sidewall of the deep trench. For this reason, the doping concentration of the surface of P-type doped region is prone to over high, resulting in a non-uniform distribution of the hole and electron concentration in the super junctions and poor voltage withstanding ability of the super junctions.
In view of this matter, the main objective of the industry in the current stage is to lower the doping concentration of the surface of the doped region used to form the super junction, so as to solve the problem of non-uniform distribution of hole and electron concentration in conventional super junction structures.